The above recited pending application is directed to a tree harvester chain saw having a guide bar configured to slidably mount onto a bar holder of the saw. The invention induces proper mounting (use of supporting pins) which renders the bar less likely to break in an accident and provides for quick removal and replacement in the event a bar breaks. With the chain removed, the bar readily slides free of the bar holder and a new bar slides into its place.
The present invention is directed to alternate configurations for such a guide bar and to a further modification and improvement to the guide bar of that invention.
As concerns tree harvesters, the forces that are available to a tree harvester operator are great and can readily break guide bars and bar holders when applied under the right conditions. Ideally when operating a tree harvester, the maximum force applied to the bar and bar holder while cutting is about 100 lbs. and both bar and bar holder will withstand such forces for a long period of use. However, it is quite typical that the ideal conditions are interrupted by what is here referred to as accidents. An accident occurs, for example, when an upper portion of the tree being cut slips in the tree harvester grapple and the chain and guide bar are pinched between the upper and lower portions of the tree. The operator has limited means by which to free the chain and bar and often he simply applies the greater power of the tree harvester to pull the bar free of the tree. That force can readily break the chain and bar and will often be done intentionally so as to allow repairs and continuation of the tree harvesting operation. The operator carries extra chain loops and extra guide bars as they are most subject to wearing and require periodic replacement in any event. Thus if the chain and/or guide bar breaks, the operator can effect repair and return of the harvester to operative condition without undue delay.
Whereas the preferred situation is that no accidents occur and thus no interruptions for repair, it is far more preferred that when a damage causing accident does happen, the guide bar will break rather than the bar holder. The bar holder is expected to last for years (as compared to the wear rate of a bar, e.g., one to three weeks) and the cost of a replacement bar holder is perhaps ten times that of a bar. Replacement of the bar holder is more complex and time consuming and most often an extra bar holder is not readily available. Thus the out of service cost for breaking a bar holder is far greater than is the breaking of the bar.
As indicated, ideally there are no accidents. However, accidents (of the type described above) do happen. In the event of an accident, it is preferred that nothing breaks. The bars can be made sufficiently strong to resist breaking in many types of accidents but an occasional accident will exceed the strongest bar and either the bar or the bar holder will break.
It is accordingly a further objective of the present invention to provide a bar that resists breaking but will break before the applied force is so great as to break the bar holder.